Action Points

Note that this observational study found an association between higher reported antioxidant consumption and diabetes incidence in women.

Be aware that results of studies based on food-frequency questionnaires have rarely been validated in randomized trials.

A diet high in antioxidants may help protect against diabetes, a new study found.

Among middle-aged women, those in higher quintiles for total antioxidant capacity reported an associated lower risk for the development of type 2 diabetes versus women in the lowest quintile (P<0.0001 for all), according to Francesca Romana Mancini, PhD, of the French National Institute of Health and Medical Research in Paris, and colleagues.

However, this risk-reduction association plateaued when total antioxidant capacity reached 15 mmol per day, the researchers reported in the study, online in Diabetologia.

"We know that diet plays a major role in the prevention of type 2 diabetes, but we are constantly looking for innovative ways to characterize someone's diet that could help him or her adopt healthier food choices," the senior study author, Guy Fagherazzi, PhD, told MedPage Today. "Studying the total antioxidant capacity of the diet offers this possibility.

"It is quite well established in the literature that some foods rich in antioxidants -- coffee, vegetables, foods rich in vitamin C or E, etc. -- are associated with a lower risk of developing type 2 diabetes, but these studies looked only at isolated nutrients or food groups, not at the total antioxidant capacity of the diet."

The team collected data on 64,223 older women (mean age of 52 ± 7 years) with dietary information who were included in the E3N-EPIC cohort, which was aimed at assessing risk factors for cancer and other chronic diseases such as diabetes. Exclusion criteria included pre-existing cardiovascular disease, pre-existing diabetes, and potential pre-existing but not diagnosed diabetes, as well as pre-existing cancer.

During a 15-year follow-up, 1,751 women were diagnosed with type 2 diabetes, identified via self-reporting and insurance drug reimbursement information. Dietary data was collected via a 208-item self-report questionnaire. An estimated antioxidant capacity of foods was identified with the ferric ion-reducing antioxidant power method, which was based upon the single-electron transfer method. However, coffee was excluded from the total antioxidant capacity from diet, because, as the authors wrote, "there is no consensus on whether the antioxidants present in coffee are actually absorbed, and because coffee has such a high antioxidant content that it would drive the association with type 2 diabetes."

In a sensitivity analysis including antioxidants from coffee, the association with type 2 diabetes prevention was still apparent, although slightly weakened among those who consumed less than 247 mL per day of coffee (P=0.003):

11.30-13.93 mmol/day (Q3): HR 0.70 (95% CI 0.57-0.85)

13.94-17.55 (Q4): 0.62 (0.50-0.77)

>17.55 (Q5): 0.61 (0.48-0.78)

The relationship was not statistically significant among those who consumed over 247 mL per day of coffee.

Fagherazzi said that he and his group were not surprised by the findings: "We were expecting to observe a decreased risk of diabetes in people with a diet rich in antioxidants. Moreover, we have shown that this decreased risk was observed independently of various type 2 diabetes risk factors, including the total daily energy intake and body mass index. However, what we did not really expect was the plateau of risk observed above 15 mmol/day, as if the organism's capacity to absorb antioxidants from the diet was saturated."

He added that his group plans to continue researching this topic with follow-up studies. "The initial objective of this work was to provide new evidence in terms of primary type 2 diabetes prevention. Now we will focus on tertiary prevention: we will now evaluate if a diet rich in antioxidants is associated with a lower risk of diabetes-related complications (cardiovascular diseases, retinopathy, nephropathy) in our E3N-AfterDiab study composed of 3,500 women living with type 2 diabetes."

The study was supported by a grant from the World Cancer Research Fund and by a grant for the E4N study from the Agence Nationale de Recherche. The validation of women with potential diabetes was supported by the European Union InterAct project.

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